Updating Adobe Reader without changing file associations

I am attempting to deploy Adobe Reader X throughout our organization. I created a package using the Adobe Customization Wizard X and it works great. However, some of our users have both Adobe Reader and Acrobat (lots of different versions from 5-9) installed on the same machine. When Reader X installs, it always sets itself as the default application for PDFs. This is usually not what the user wants if they have Acrobat installed.

The customization wizard only has two options here, either make Reader the default, or the installer will decide which will be the default. However, both of those seem to result in Reader becoming the default (all of our Acrobat Pro versions are older than Reader X, so maybe that's why?).

What I would like to do is simply check before installing reader to see what the user has set as the default, and then set it back to that once Reader has been installed. But I am still not quite sure which reg key is the one to check for this? If I look under HKCR, I see .pdf which shows a default value of AcroExch.Document. If I find that, I notice it has a Shell\Open\command key with a default of the path to Acrobat.exe. If I change this to something else, it doesn't seem to affect what program opens when I double click a PDF file. But there is another key called AcroExch.Document.7 with the same shell\open\command key and if I change that one, it does affect which program opens the PDF. So if I just write a script to change this key once Reader X has been installed, will that work or does it depend on what version(s) of Adobe products they have installed on their system?